Society is increasingly interested in treating everyone fairly. As our sense of fairness has evolved, we have had campaigns against racism, sexism, agism etc. However, most countries operate an immigration policy which is highly unfair without any public outcry.
All countries have some form of rules about who is allowed to live in the country. Occasionally the rules will include some criterion which might be considered fair e.g. your criminal record, your professional qualifications , etc. - but the most important factor in most countries decision is the totally arbitrary fact of where you and/or your parents were born. Surely the location of where you were born has very little bearing on whether or not you will be an valued member of society.
I appreciate that there are circumstances where the number of people wanting to live in a certain area is above what can be catered for. For example, in Ireland there was until recently a problem where too many people wanted to live in the greater Dublin area and this put strain on the infrastructure. However, when the migration is happening within the country the proposed government response is normally a positive one (e.g. improving job prospects in the relatively under populated west) - imagine the outcry which would result if the government proposed that only people born in Dublin could live in Dublin and put immigration controls on the main roads leading to Dublin.
When too many people from Eastern Europe are migrating to the more developed countries in the West, why does everyone assume that the solution is to put unfair restrictions in place on immigration. Why not instead focus on making living and working conditions more attractive in Eastern Europe? I do realise that there are concerns about the potential for people to abuse social welfare systems, but we could put reasonable restrictions on who is allowed to qualify for social welfare payments without the need to maintain complex immigration controls.
If we abolished immigration controls, the only real losers are the people who have the boring job of checking passports in our airports. If too many job seekers came to Ireland looking for work, they would soon realise that they were in an overcrowded job market and naturally choose of their own accord to move somewhere where they had better employment prospects.